promise.js

// Anti-pattern: creating a new promise instead of continuing an existing chain
insert() { // method inside ES6 class
  return new Promise((resolve, reject) => {
    this.db.collection(this.collection).insert(this.fields)
    .then((modelDocument) => {
      this.fields = modelDocument;
      this.notifyObservers({event: "created", model: this});
      resolve(modelDocument)
    }).catch((err) => {
      reject(err)
    })
  });
}

// Better:
insert() {
  return this.db.collection(this.collection).insert(this.fields)
  .then(modelDocument => {
    this.fields = modelDocument;
    this.notifyObservers({event: "created", model: this});
    return modelDocument;
  });
}

// More information on promises: http://www.2ality.com/2014/10/es6-promises-api.html